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Versatile Human Stem Cells Created Without Embryos

Two separate research teams have figured out how to "reprogram" cells with just a handful of genes to give them the characteristics of embryonic stem cells. The breakthrough may eventually put to rest the ethical controversy surrounding stem cells.

Researchers have been hoping to harness the therapeutic potential
of cloning ever since the cloning of Dolly the sheep in 1997.
Cloning entails taking the nucleus—the compartment that
contains the DNA—from an adult cell and putting it into
an egg from which the original nucleus has been removed. The
egg then "reprograms" the adult nucleus so that the cell behaves
like an embryo but has the genes of the adult cell.

When an embryo like this is implanted into a uterus, as with
Dolly, the process is called reproductive cloning. In another
strategy, called therapeutic cloning, the embryo can instead
be used to create stem cells that are genetically identical to
a patient. Since embryonic stem cells have the ability to form
virtually any cell type in the body, those taken from a cloned
embryo could potentially be used to treat many diseases. Therapeutic
cloning has garnered a great deal of attention over the past
few years, but until now it had only been achieved in the mouse.

Researchers reported in Nature on November 22, 2007,
that they successfully isolated 2 embryonic stem cell lines from
cloned embryos made using cells from the skin of an adult rhesus
macaque. Before this new study was published, Nature asked
another group of researchers to confirm that the stem cells were
genetically identical to the donor skin cells. Their report,
published in the same issue of the journal, confirms that therapeutic
cloning has now been accomplished in primates for the first time.

The team that isolated the embryonic stem cell lines was led
by Dr. Shoukhrat Mitalipov at Oregon Health and Science University
in Portland. Their work was supported by NIH's National Institute
of Neurological Disorders and Stroke (NINDS), National Institute
of Child Health and Human Development (NICHD) and National Center
for Research Resources (NCRR).

The stem cells, the researchers showed, could turn into heart
or nerve cells in the laboratory, and had other characteristics
of established embryonic stem cell lines. One of the keys to
the research team's success was that they used a newer, more
precise technique for removing the egg's genetic material.

Although this study proves that the therapeutic cloning of primates
is possible, there are still many hurdles to be overcome. In
particular, the efficiency of the process will have to be improved
before the technique could be applied in the clinic using human
cells. The team injected 314 eggs to get the 2 stem cell lines—an
efficiency of less than 1%.